On August 20, 1996, at 1715 Pacific daylight time, a homebuilt Westcott Glasair I-FT, N289W, operated by and registered to the pilot as a 14 CFR Part 91 personal flight, experienced a loss of engine power shortly after takeoff from Pierce County-Thun Field, Puyallup, Washington. The pilot initiated a forced landing to a city road where, during the landing roll, the airplane collided with two vehicles. Visual meteorological conditions prevailed at the time and no flight plan was filed for the local flight. The airplane was substantially damaged and the commercial pilot was not injured. One person in one vehicle was seriously injured, the other person in another vehicle was not injured. The flight departed from Pierce County approximately one-half hour prior to the accident. During a telephone interview and subsequent written statement, the pilot stated that the purpose of the flight was to test a newly installed accelerometer. The pilot spent some time performing various maneuvers before returning to the airport to practice touch-and-go landings. After the second takeoff, the pilot stated that at approximately 300-400 feet above ground level, the engine lost power. The pilot was unable to restart the engine and initiated a forced landing. The pilot stated that an open field was unattainable and there were no other suitable landing sites so he elected to aim for and land on a roadway. During the touchdown, the airplane collided with two occupied vehicles. An inspection of the engine revealed that the inlet screen to the carburetor air box had been fabricated with an approximate half-inch square metal meshing. The wire on the screen broke, allowing the foam air filter to be sucked into the throat of the carburetor.